Sea Robin

These distinctive-looking fish are sometimes sought after by fishers and are, by some, considered good to eat. They were first discovered in 1815. Their most common name, sea robin, comes from the orange-red color of their skin. The other commonly used name that one is likely to see, gurnard, comes from an unusual croaking noise the fish make when they’re caught. They are normally found at the bottom of the sea, due to their feeding style.

There are three subfamilies of sea robin. They are:

• Prionotinae
• Pterygotriglinae
• Triglidae
  

The first, Prionotinae, grows to around seventeen inches or forty-three centimeters. They are commonly found off the coasts of the Americas, in both the Atlantic and Pacific Oceans. 

Pterygotriglinae is found in the Indo-Pacific and is more closely related to Prionotinae than it is to Triglidae. It has twenty-seven vertebrae, unlike the other subfamilies of sea robin. 

The Triglidae subfamily includes the four genera: 

• Chelidonichthys
• Eutrigla 
• Lepidotrigla
• Trigla 

Credit: Daiju Azuma

Appearance 

Sea robins are known for their colorful skin and pectoral and dorsal fins, and bony heads which give them a notable appearance. Their two dorsal fins contain spines, the first between seven and eleven and the second up to twenty-three. They are considered to have a spiny head.

The largest species of sea robin can reach nearly thirty inches, or seventy-five centimeters, in length, while the smallest only grows to a maximum of four inches. Some species of sea robins have armored plating on their skin and hard, unusually solid skulls. This is one reason why this unique fish is not more commonly sought after by fisheries. Getting through the plating can be a difficult task.

The unusual-looking fish are also notable for their pectoral fins, or fin rays, that are used to walk along the ocean floor. They utilize these as feelers so they can survey their surroundings. These fanlike pectoral fins or walking rays, help sense their prey, such as crustaceans, mollusk, and other prey that inhabit the sea floor. It also makes them good swimmers. Their mouths are generally positioned below their noses or snouts. The snout is itself notable for the two spines at its tip. This adds to the sea robin’s overall memorable appearance. 

Many different types of sea robins have beautiful patterns. The common sea robin is not the only variation. There are variations such as the striped sea robin, bighead sea robin, and the leopard sea robin. The European tub gurnard is known for its reddish-brown color. Sea robins also have a unique muscle system that allows them to make noise with their swim bladder. This noise has been described as frog-like.

Credit: Hamid Badar Osmany

Habitat

Sea robins are bottom dwellers. This means that they are commonly found along the bottom of tropical oceans, around 660 feet or 200 meters. They are found in tropical waters around the world but are most common in the Atlantic Ocean, in the stretch between Nova Scotia to the southern part of the United States around Florida. They tend to gravitate towards a sandy area so they can scan the seabed for food. In the colder months, sea robins migrate southward, and into deeper waters.

Diet 

Scientists have also observed sea robins using their unusual pectoral fins to detect prey on the sandy ocean floor via a process known as chemoreception. This allows them to sense the amino acids in other creatures’ bodies. They are not picky eaters and have been known to eat everything from worms to mollusks, shrimp, amphipods, and small crustaceans. Often, they dig into the seafloor and pull out anything they find. 

Adults have also been seen eating seaweed and sand, but sea robins are classified as carnivores. As they age, they do become somewhat more specific in what they choose to eat. Younger sea robins, especially of the northern variety (Prionotus carolinus), are known to have very diverse diets. 

Interestingly anglers will use a plethora of bait to catch sea robins. They have been known to use anything from crabs, and small fish, to a wide variety of invertebrates. Some fishermen know the sea robin as a nuisance, because they are unpleasant to handle, and they steal bait in search of food.

Reproduction 

Sea robins breed in open areas near the seafloor from late spring through the summer months. July, August, September, and October tend to be the most optimal time for breeding. Adults have been observed remaining in the warmest waters during the summer in order to allow their eggs to hatch in water that’s around 70 degrees. 

Most sea robins reach maturity at around two to three years old, but some species, like the northern sea robin, can produce eggs at only one year old. Interestingly, when mating season is going on, the normal grunting sound the sea robin is known for changes into a more staccato sound. 

Their eggs are externally fertilized and, when produced, are triangular in shape at around 0.2mm to 1.0mm long. After laying their eggs, they hatch within sixty hours. Adult sea robins have no interaction with their young after laying their eggs. 

Threats 

Sea robins, like many other marine species, are threatened by the practice of bycatch. That is when a species is caught up in a fishing net that is not intended for them and then tossed back into the water, dead. While sea robins are common in the world’s oceans, bycatch is a harmful process that can have long-term consequences. 

Facts about Sea Robins 

• They make an unusual croaking sound when caught. 
• They have colorfully-patterned fins and a reddish body. 
• Their bodies are covered with bony plates. 
• Sea robins are often caught as bycatch. 
• They mate during the summer months. 
• Sea robins can use their pectoral “walking fins” to travel along the ocean floor. 
• They’re common from Nova Scotia to Florida. 

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